There are usually designated smoking areas in public places such as Lido Restraunt and main dining room. Hal allows you to smoke in your cabin and most other areas such as Casino, Bars,Pool,etc. I not sure of other lines has I'm Hal Aholic, Love HAL.

Kris,
At the moment the only non smoking ships are the Carnival Paradise, and all the Renassance Cruise Line ships (though Ren is changing to allow limited smoking areas).
All others have designated smoking areas in the lounges, and on deck, and smoking is allowed in all cabins.
Most do not have smoking sections in their dining rooms. Holland America and Seabourn being exceptions that I know of... plus, I believe Costa Cruise Lines.

With the exceptions noted above, and the Radisson fleet (last I knew), all dining rooms are non-smoking. I don't know of any show lounges where smoking is permitted.

Generally, smoking is permitted AT bars (like, sitting on the stools) and the lounges are divided between smoking and non-smoking. If a public area spans the entire width of the ship, one side will be designated smoking, the other non-smoking. Usually.

One hint: If you smoke something other than the most popular brands, take your own.

Most (if not all) Celebrity ships also have a cigar lounge.
This is one place in particular that you can smoke to your hearts content. Celebrity allows smoking in many public areas,port for smokers,starboard for non. There is no smoking however in the
dining rooms or the show lounge.